1. Field of the Invention
The present invention relates to the field of injection devices and in particular syringes which are used to inject drugs and other medications into patients and which may later be used by intravenous drug users. More particularly, the present invention relates to a specialized syringe which can be used only once and is thereafter self-annulling to thereby render the syringe inoperative after it has been used only once. The present invention is concerned with a self-annulling syringe which is rendered inoperative by its own action without requiring any active destruction force from the user or medical doctor. The use of such syringes is particularly valuable to reduce the opportunity for intravenous drug users to share syringe needles and thereby spread blood-transmitted infectious diseases.
2. Description of the Prior Art
AIDS is being spread by the multiple reuse of syringes. Intravenous drug users recover discarded syringes that have been used for medical purposes and reuse and share them between infected and un-infected individuals to inject drugs such as heroin. Many inventors have conceived various embodiments to syringes but only one is intended to inactivate a syringe after it has been used once. The closest prior art relating to the principals employed in the present invention are as follows:
1. U.S. Pat. No. 4,781,683 issued to Wozniak et al and assigned to Johns Hopkins University. The Patent is entitled "Single-Use, Self-Annulling Injection Syringe" and issued on Nov. 1, 1988.
2. U.S. Pat. No. 3,982,538 issued to Sharpe on Sept. 28, 1976 for "Safety Valves For Protection Against Liquid Contamination".
3. U.S. Pat. No. 3,373,743 issued to Saffir on Mar. 19, 1968 for "Disposable Hypodermic Syringe".
4. U.S. Pat. No. 3,941,128 issued to Baldwin on Mar. 2, 1976 for "Fluid Dispensing Arrangement".
5. U.S. Pat. No. 2,798,487 issued to Ferguson on July 9, 1957 for "Syringe Assembly".
6. U.S. Pat. No. 4,449,693 issued to Gereg on May 22, 1984 for "Catheter Check Valve".
7. U.S. Pat. No. 2,893,390 issued to Lockhart on July 7, 1959 for "Hypodermic Syringes".
U.S. Pat. No. 4,781,683 to Wozniak discloses a syringe which includes within it a hydrophilic expansion plug 18 that is positioned in the fluid channel of the syringe. The hydrophilic expansion plug will swell when exposed to water contained in the medication and the inventors allege that this expansion will occlude the fluid channel, thereby preventing multiple use of the syringe and needle. While the intent is to have the plug completely fill the chamber it is in, there is no assurance that the passageway to the needle will be completely occluded and therefore it may be possible to still use the syringe, although with much less drug injecting capability, even after the plug has expanded to its full volume. The inventors of the present invention have determined that it takes only one or two thousandths of an inch gap to permit medication or drugs to flow from the drug retaining chamber to the needle. While the inventors in the Wozniak patent allege that the needle was rendered inoperative after only 5 minutes (see column 4, lines 17 through 36), it is believed that in general the bulk of and hydrogel composition of the plug in Wozniak may not completely fill all of the gap area and may leave one or two thousandths of an inch which is sufficient for drugs to be injected through the needle. In addition, with time the gel will dry and will lose some of its expansion, thereby leaving open the opportunity for reversal in the process and the creation of a one or two thousandths inch gap. In addition, not all medicines are water based and the Hydrophilic Expansion Plug 18 may not swell and occlude the fluid channel when exposed to other medicine fluids such as sesame oil.
An additional problem with the Wozniak Patent is that the device is not entirely tamper proof. Referring specifically to column 4 beginning on line 37, the Patent text states "FIG. 3 is a cross-sectional view of a single use, self-annulling syringe with a separable needle body. In this embodiment, the hydrophilic expansion plug 28 is located in a separate needle body 30. A step 32 in the needle body 30 is used to secure the hydrophilic expansion plug 28. There is sufficient elasticity in the step 32 and plug 28 to enable the plug to be press fit passed the step and locked into place." However, this same apparatus permits the device to be removed from the needle and have the hydrophilic expansion plug picked out with the scraping type device so that the needle can be reused.
U.S. Pat. No. 3,373,743 to Saffir discloses a disposable hypodermic syringe which includes within it a closure member 48. Closure member 48 is essentially an elastic piece of material which is more clearly illustrated in FIGS. 3, 6 and 7. The object of the closure member 48 is to provide a blocked passage so that medication in the syringe cannot enter into the needle. The specific intent of this patent is to create a situation where medications can be placed in the syringe and then left there for a period of time since the medication will be blocked by closure member 48 and thereby be prevented from coming in contact with the needle and therefore possibly contaminating the medication and/or corroding the needle. When in use, the plunger which moves the medication further toward the closure member under pressure causes it to distort so that the medication can pass through the openings in the closure member between the radial ribs. In this case, the closure member with radial ribs serves to temporarily block the passage of medication or drugs until distorted so that fluid can pass between the ribs. This is not a single use syringe since the syringe can be used over and over again after the closure member has become distorted.
U.S. Pat. No. 2,893,390 to Lockhart relates to a Hypodermic Syringe which includes a piston plug possessing grooves. The idea of this patent is to once again have a syringe filled with medication and then stored in a manner such that the plug blocks the passage of medication to the metal needle in order that the medication will not become contaminated and so that the needle will not corrode. When in use, the plunger causes the plug to move forward so that the grooves permit the passage of medication to the needle. Once again, after the sliding partition plug 765 has been moved forward, the syringe can be used over and over again.
U.S. Pat. No. 3,941,128 to Baldwin also embodies the same concept of having a plug which blocks medication which has been placed in a pre-filled syringe from coming in contact with the needle until such time as the plunger is depressed in which case the plug is moved to an operative form so that fluid can pass to the needle.
U.S. Pat. No. 3,982,538 to Sharpe employs the concept of a safety valve in a pipette in which the valve swells up in the presence of unwanted fluid and occludes passage of liquid.
U.S. Pat. No. 2,798,487 to Ferguson and U.S. Pat. No. 4,449,693 to Gereg show various plug arrangements or check valve arrangements.
Therefore, while various devices in the form of plug or check valve members have been known to occlude passages, the prior art embodiments do not provide an entirely satisfactory solution for causing the syringe to become inoperable. The use of a plug which merely expands to a greater size does not assure that the passageway to the needle will be entirely occluded and therefore it is possible that the syringe may still be operable for multiple uses although the effectiveness of the syringe is reduced. Therefore, a significant need exists for an improved mechanism by which there is assurance that after a single use, the syringe will become completely inoperable from further use.